Vehicle security system

ABSTRACT

The security system comprises a coil (34) close to the vehicle ignition lock (38), a control unit (10) for energizing the coil and a transponder which comprises a coil (32), a transistor (30) and a transmitter (24) and a power supply (26). In use the coil (32) picks up a conventional alternating magnetic signal emitted by the coil (34), and provides sufficient power to activate the transistor (30) which connects the power supply (26) to the transmitter (24) causing it to transmit an enabling signal to the control unit. The control unit may be programmed to re-mobilize the vehicle engine on receiving of the correct signal.

The present invention relates to vehicle security systems, and inparticular to those including `passive remobilization` which ensuresthat the vehicle will not remain immobilized if the driver has enteredthe vehicle and wants to start it using the proper key.

Passive re-mobilization systems are known, for example from EP 0 521 547and WO 93/02897. WO 93/02897 discloses a security system in which atransmitter unit has an encoder and a transmitter which can be operatedmanually to transmit codes from the encoder. The transmitter unit alsohas electrical contacts through which the code from the encoder can beconducted to co-operating contacts near the vehicle ignition switch tore-mobilize the vehicle when the key is in the ignition lock.

It is an aim of the present invention to provide an improved securitysystem which overcomes various problems with the known systems describedabove.

Accordingly the present invention provides a vehicle security system,comprising: a portable transmitter unit comprising a transmitter fortransmitting a coded signal, a power source for the transmitter, andmanual actuation means for causing the transmitter to transmit the codedsignal; a receiver mounted on the vehicle; control means arranged toenable or disable a component of the vehicle in response to receipt ofthe coded signal by the receiver; an ignition lock on the vehicle; a keyfor operating the ignition lock; and means for producing an energy fieldif the key is used in the ignition lock while said component isdisabled, characterized in that the transmitter unit further comprisesswitch means which can be operated by the energy field to connect thetransmitter to the power supply to cause the transmitter to transmit thecoded signal for reception by the receiver.

This arrangement can meet the above aim in a simple and cost-effectivemanner.

Preferably the energy producing means is mounted in the vehicle near tothe ignition lock.

The use of the key required to cause transmission of the signal bycomprise turning or otherwise moving the key to a particular position inthe lock, or simply inserting the key into the lock, or any othersimilar action depending on the nature of the lock and key system.

Preferably the system further comprises key use detection means fordetecting use of the key in the ignition lock wherein the control meansis arranged to produce the energy field only if the detection meansdetects use of the key in the ignition lock.

Preferably the transmitter unit is attached to the key.

Said energy field may comprise an alternating magnetic field orelectromagnetic radiation, in which case the means for producing saidenergy field preferably comprises a coil, and the switch meanspreferably includes a coil for producing an electromotive force inresponse to said energy field.

Alternatively the energy field may comprise a magnetic field ofsubstantially constant direction, in which case the source of themagnetic field may be an electromagnet or a permanent magnet. In thiscase the switch means preferably has first and second electrical contactmeans at least one of which is made of a ferromagnetic material suchthat it will become magnetized and be attracted towards the other in thepresence of said magnetic field. Such a switch means may comprise a reedswitch and said at least one contact may comprise a reed thereof.Alternatively the switch means may comprise a hall effect device orother electronic device operated by a magnetic field.

Preferably the control means is arranged to unlock at least one door ofthe vehicle in response to receipt of an unlock signal from thetransmitter unit if said unlock signal is produced by the manualactuation means, but not if said unlock signal is produced as a resultof use of the key in the ignition lock.

Indeed the present invention further provides a vehicle security systemcomprising an ignition lock and a key for operating the lock, atransmitter for transmitting a coded unlock signal, first actuationmeans for causing the transmitter to transmit the coded unlock signaland second actuation means for causing the transmitter to transmit thecoded unlock signal if the key is used in the ignition lock, wherein thecontrol means is also arranged to unlock at least one door of thevehicle upon receipt of an unlock signal from the transmitter if saidunlock signal is produced by the first actuation means, but not if saidunlock signal is produced by said second actuation means.

The first actuation means may be a manual actuation means such as apush-button.

Preferably the second actuation means is actuated by a signal from thecontrol means and the control means is arranged to determine whether theunlock signal was produced by the second actuation means by timing thedelay between the sending of said signal and receipt of the unlocksignal.

This arrangement is to allow for a situation where the driver hasentered the vehicle and locked the doors for his own personal safety,and then starts the vehicle. In this situation the doors are notunlocked again by the system when the transmitter transmits the codedsignal to enable the component of the vehicle. However the transmitterwill still cause the doors to be unlocked (or locked) when it is usedoutside the vehicle.

The present invention still further provides a method of matching atransmitter unit which is arranged to transmit coded signals with acontrol unit forming part of a vehicle security system, the methodcomprising the steps of passing parameters of the coded signal from thecontrol unit to the transmitter unit and storing them in memory in thetransmitter unit.

Preferably said parameters comprise at least one encryption parameter.Alternatively they may comprise a code or a part thereof.

Preferred embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings inwhich:

FIG. 1 is a diagrammatic view of a vehicle security system in accordancewith a first embodiment of the invention.

FIG. 2 is a diagrammatic view of a vehicle security system in accordancewith a second embodiment of the invention,

FIG. 3 is a diagrammatic view of a reed switch in the embodiment of FIG.2, and

FIG. 4 is a diagrammatic view of a vehicle security system in accordancewith a third embodiment of the invention.

Referring to FIG. 1, in the first embodiment of the invention, asecurity control unit 10 which is mounted on a vehicle 11 has variousoutputs 12 enabling it to immobilize the engine 14 of the vehicle, bydisabling the fuel injection system 15, and operate locks 16 on thevehicle doors 18. The control unit 10 is connected to a radio frequency(RF) receiver 20 and is arranged to unlock the doors 18 and re-mobilizethe engine 14 upon receipt of a coded RF unlock signal, and to lock thedoors and immobilize the engine upon receipt of a coded lock signal. Anignition key 21 for the vehicle has an RF transmitter unit 22 attachedto it. The transmitter unit 22 comprises an RF transmitter circuit 24arranged to send coded RF unlock and lock signals, a power source 26 forthe transmitter circuit, and an unlock button 28 for activating thetransmitter manually to send the unlock signal by connecting the powersupply 26 to the transmitter circuit 24. A lock button (not shown) isalso provided to cause the transmitter to send the coded lock signal.The transmitter unit further comprises a transistor 30 and a coil 32connected so that electromotive force induced in the coil can be used tocause the transistor to connect the power supply to the transmittercircuit 24.

A second coil 34 is connected to the control unit 10 and is housed in acowl 36 of the vehicle, close to a vehicle ignition lock 38. The controlunit 10 is connected to the normal electrical outputs from the ignitionlock 38 so that it can sense when the ignition key is present in theignition lock, and when it is in the auxiliary, ignition and crankpositions.

Normally when the driver approaches the vehicle he will re-mobilize theengine 14 and unlock the doors 18 by pressing the unlock button 28.However if he has unlocked the doors using the key 21 in the door locks16 the engine may still be immobilized when he enters the vehicle. Thisis particularly likely to happen if the security control unit 10 isprogrammed to immobilize the engine automatically when the driver leavesthe vehicle. The control unit 10 is therefore arranged to detect thesituation when the engine is immobilized and the key 21 is turned to theauxiliary position in the ignition lock 38.

In this situation the control unit passes an AC current through the coil34 which induces a current in the coil 32 in the transmitter unit 22.This causes the transistor 30 to connect the power supply 26 to thetransmitter circuit 24 which transmits its coded unlock signal. Thissignal is picked up by the receiver 20 and compared by the control unit10 to a code stored in memory. If the codes are the same the controlunit re-mobilizes the engine 14 by re-enabling the fuel injection system15, and the driver can start the car in the usual way.

If for security reasons the vehicle user should enter the vehicle andlock the doors 18 mechanically (by depressing the usual locking buttonon the door) it is important that the doors do not unlock when the codedunlock signal is transmitted to the control unit 10 as the ignition isswitched on. The control unit 10 is therefore programmed to recognizewhen the coded unlock signal has been sent as a result of use of the key21 in the ignition lock 38, and to leave the state of the vehicle doorlocks unchanged whilst still re-mobilizing the engine. Because thecontrol unit 10 causes the coil 34 to transmit its signal it candetermine whether the unlock signal has been produced in response to asignal from the coil 34 simply by timing the delay between sending thesignal from the coil 34 and receipt of the unlock signal. If the delayis less than a predetermined time then the door locks can be left in thelocked state. Alternatively the control unit could be arranged to unlockthe doors only of the unlock signal was received and the key was notdetected in the ignition lock.

When the ignition key 21 is removed from the ignition lock 38, and theignition is thus disabled, the control unit 10 automatically immobilizesthe engine; thereafter the vehicle doors 18 may be locked mechanicallyor by using the lock button on the transmitter unit 22.

The transmitter circuit 24 includes a memory in which a code is storedtogether with an encryption algorithm which encrypts the code before itis transmitted as a coded signal. The control unit 10 has acorresponding memory in which the code and the algorithm are alsostored. The coded signal is therefore deciphered using the algorithmbefore it is compared with the code in the memory of the control unit10. When a transmitter unit needs to be matched to the vehicle, thecontrol unit 10 is made to transmit the encryption algorithm, precededby an identification code, to the transmitter unit 22 which recognizesthe identification code and stores the following algorithm in itsmemory. The transmitter unit 22 is then used to transmit a code storedin its memory, using the encryption algorithm, to the control unit 10five times within five seconds. The control unit recognizes this as aninstruction to store the code, after deciphering, in its memory,overwriting any code which is stored there already. In this way auniquely coded transmitter and a control unit having one of a largenumber of possible encription algorithms can be matched up forsubsequent use.

It will be appreciated that instead of a whole encryption algorithm, oneor more encryption parameters or a part or the whole of the code couldbe transmitted from the control unit to the transmitter.

Referring to FIG. 2, the second embodiment of the invention is similarto the first, and corresponding features are indicated by the samereference numerals preceded by a 1. In place of the coil 30,amagnetically operated switch means in the form of a reed switch 130 isprovided which can activate the transmitter circuit 124 as describedbelow. The reed switch 130 is shown in more detail in FIG. 3 and has twocontacts 131, 131a which are made of a flexible magnetic material. Thecontacts 131, 131a are supported such that they normally lie parallel toone another but are spaced a small distance apart.

When the control unit 110 detects the situation when the engine 114 isimmobilized and the key 121 is turned to the auxiliary position in theignition lock 138, the control unit energizes the coil 134 by passing aDC current through it, thereby causing it to become magnetized. Themagnetic field produced by the coil 134 is of constant direction andwill magnetize the contacts 131, 131a of the reed switch 130, which willbe attracted to one another, connecting the power supply 126 to thetransmitter circuit 124.

As a variation on the second embodiment described above with referenceto FIGS. 2 and 3, the coil 134 could be connected to a simple DC powersupply via a switch which is operated by turning the key 121 in theignition lock 138. A positive temperature coefficient (PTC) device or asuitable timing device could also be used to turn off the power to thecoil 134 after a predetermined time to ensure that it was only energizedfor long enough to re-mobilize the engine.

Referring to FIG. 4 the third embodiment of the invention differs fromthe second in that the transmitter circuit 224, power source 226 andreed switch 230 are mounted on the head 240 of the ignition key 221.Also, instead of an electromagnet, or coil, a permanent magnet 234 ismounted in the cowl 236 close to the ignition lock 238. In this waythere is no need for monitoring the position of the key in the ignition.Instead the permanent magnet is made of a suitable strength such thatthe reed switch 230 will be closed whenever the key is brought within aspecific range of the magnet 234. This range can be of the order of afew centimeters so the switch will generally only close when the key isactually inserted in the ignition lock 138.

We claim:
 1. A security system for a vehicle which includes a component,the system comprising: a portable transmitter unit comprising atransmitter for transmitting a coded signal, a power source for thetransmitter, and manual actuation means for causing the transmitter totransmit the coded signal; a receiver for mounting on the vehicle;control means arranged to enable or disable said component in responseto receipt of the coded signal by the receiver; an ignition lock for thevehicle; a key for operating the ignition lock; and means for producingan energy field if the key is used in the ignition lock while saidcomponent is disabled, wherein the transmitter unit further comprisesswitch means which can be operated by the energy field to connect thetransmitter to the power supply to cause the transmitter to transmit thecoded signal for reception by the receiver.
 2. A system according toclaim 1 wherein the energy producing means is mounted in the vehiclenear to the ignition lock.
 3. A system according to claim 1 furthercomprising key detection means for detecting use of the key in theignition lock wherein the control means is arranged to produce theenergy field only if the detection means detects use of the key in theignition lock.
 4. A system according to claim 1 wherein the controlmeans is arranged to produce the energy field only if the component isdisabled.
 5. A system according to claim 3 wherein the transmitter unitis attached to the key.
 6. A system according to claim 1 wherein saidenergy field is an alternating magnetic field.
 7. A system according toclaim 1 wherein said energy field comprises electromagnetic radiation.8. A system according to claim 1 wherein the means for producing saidenergy field comprises a coil.
 9. A system according to claim 1 whereinthe switch means includes a coil for producing an electromotive force inresponse to said energy field.
 10. A system according to claim 1 whereinthe energy field comprises a magnetic field of substantially constantdirection.
 11. A system according to claim 10 wherein the source of themagnetic field is an electromagnet.
 12. A system according to claim 10wherein the source of the magnetic field is a permanent magnet.
 13. Asystem according to claim 10 wherein the switch means has first andsecond electrical contact means at least one of which is made of aferromagnetic material such that it will become magnetized and beattracted towards the other in the presence of said magnetic field. 14.A system according to claim 13 wherein the switch means is a reed switchand said at least one contact comprises a reed thereof.
 15. A systemaccording to claim 1 wherein the the vehicle includes at least one doorand control means is arranged to unlock said at least one door inresponse to receipt of an unlock signal from the transmitter unit ifsaid unlock signal is produced by the manual actuation means, but not ifsaid unlock signal is produced as a result of use of the key in theignition lock.
 16. A security system for a vehicle including at leastone door, the system comprising an ignition lock and a key for operatingthe lock, a transmitter for transmitting a coded unlock signal, firstactuation means for causing the transmitter to transmit the coded unlocksignal, second actuation means for causing the transmitter to transmitthe coded unlock signal if the key is used in the ignition lock, andcontrol means arranged to determine whether the unlock signal has beenproduced as a result of use of the key in the ignition lock and tounlock said at least one door upon receipt of the unlock signal from thetransmitter if said unlock signal is produced by the first actuationmeans, but not if said unlock signal is produced by the second actuationmeans.
 17. A system according to claim 16 wherein the second actuationmeans is actuated by a signal from the control means and the controlmeans is arranged to determine whether the unlock signal was produced bythe second actuation means by timing the delay between the sending ofsaid signal and receipt of the unlock signal.
 18. A system according toclaim 9 wherein the transmitter unit includes a memory which isconnected to said coil so that at least one parameter of the codedsignal stored in the control means can be transmitted to the transmitterunit and stored in the memory thereby to match the transmitter and thecontrol unit.
 19. A system according to claim 18 wherein said at leastone parameter comprises at least one encryption parameter.